Leap second handling

Red Hat Enterprise Linux 9.2 LPAR mode

Through STP, Linux® on IBM® Z can process leap seconds from a coordinated time network (CTN) and adjust the TOD clock accordingly.

STP can schedule leap second insertions or deletions for your Linux instance. With one or more leap seconds scheduled, the Linux kernel checks, at regular intervals, whether the day for a leap second adjustment is reached.
STP schedules leap second adjustments for the end of day according to UTC.
Leap second deletion
A second is deleted at 23:59:59, that is, 23:59:58 is followed by 00:00:00.
Leap second insertion
A second is inserted at 23:59:59, that is, 23:59:59 is followed by 23:59:60.
Use the lsstp command to display information about scheduled leap seconds for your Linux instance.
Note: Do not run an NTP daemon like chrony or ntpd with STP enabled. NTP daemons can interfere with leap second handling through STP.